The fabrication of integrated circuits typically uses a number of photolithographic steps to impart a pattern on a semiconductive substrate or wafer. For example, where a layer of material, such as polycrystalline silicon or aluminum, is formed over the wafer, a layer of an organic material such as a photoresist, is subsequently formed over the material. The photoresist is then selectively exposed to an energy source and then processed to provide a pattern that is representative of the selective exposure. Thus some portions of the material underlying the photoresist remain covered while other portions are exposed. Once such a pattern is formed in the photoresist, a subsequent process is employed to replicate that pattern in the underlying material. For example, polycrystalline silicon and aluminum can be patterned using a plasma etching process that removes the exposed portions of such material, thus replicating the pattern. Once this etching process is completed, generally the photoresist is removed prior to any subsequent processing step.
While there are a variety of well known methods for removing such photoresist material, as semiconductor technology has advanced to create higher performance integrated circuits, such previously known methods are often problematic. For example, one such previously known method is commonly known as Plasma Ashing and employs an electrically induced oxygen plasma to oxidize the organic material of the photoresist into gaseous products such as carbon dioxide and water vapor. However, advanced integrated circuits are often susceptible to damage by the action of the electrical fields required to create a plasma that is sufficient for such an oxidative process. Other well known methods employ strong oxidizing chemicals in baths or use such chemicals in spraying mechanisms to remove the organic photoresist material. One such strong oxidizing material is a mixture of concentrated sulfuric acid and hydrogen peroxide, often referred to as “Pirhana.” However, while such strong chemicals are effective, they are also hazardous to the people that use them; they are difficult to dispose of after use without taking extensive measures to protect the environment; and they are not generally applicable to removing photoresist from materials such as those that encompass aluminum and other metals.
Therefore it would be advantageous to provide methods for removing organic materials, for example photoresist, from semiconductive wafers with methods that will reduce or eliminate damage to circuit elements formed thereon. It would also be advantageous if such methods did not require the use of chemicals that are hazardous to both the people that use them and to the environment.
Finally, it has been found that it is often advantageous to form a self-limiting oxide layer, that is to say a layer of oxide having a thickness that is limited by the growth of the film itself, over any oxidizable materials that are exposed to oxidizing conditions during subsequent processing. Such oxide layers are often thought of as passivating the surface of the oxidizable material, where such passivation limits the reactivity of the exposed material during a subsequent process. While such previously known methods as plasma ashing and immersion into chemical baths containing “Piranha” can and do oxidize oxidizable materials to form such oxide passivation layers, it would be advantageous to provide alternative methods for forming such layers that do not use hazardous materials and/or potentially damage advanced semiconductor devices.